Abstract
To compare the fat-stability tests commonly employed for the evaluation of rancidity, the decomposition rate of tocopherol homologues (Toc) contained in soybean, corn and rapeseed oils was measured by active oxygen method (AOM), oven test, organoleptic method and weighing method. The Toc content was determined by the high performance liquid chromatographic method.
The results obtained were as follows:
1) AOM test: It was found that there was a good correlation between the decrease of Toc contents and the increase of peroxide value (POV) after the induction period. The decomposition rate of these Toc was the following order; α<γ<δ. When POV of soybean oil reached 100, the decamposition of α-Toc was about 85% and this of γ-Toc was 20%, while this of δ-Toc was only 4%.
2) Oven test: Rancid point, which is designated to be 3 by flavour score by organoleptic evaluation, showed a well coincide with the break time which is also designated to be the point at where the POV begins to increase. It was also found that, at this rancid point, the decomposition of Toc began.
3) Weighing method: The induction period, the point at where the weight increase by 0.5%, of soybean and corn oils was 275 and 400 hours, respectively, and before this point, Toc were completely decomposed.
